<!DOCTYPE html>
<html lang='en'>
<head>
  <meta charset='UTF-8'>
  <meta http-equiv='X-UA-Compatible' content='IE=edge'>
  <meta name='viewport' content='width=device-width, initial-scale=1.0'>
  <title>React Document</title>
  <style>
    .list {
      width: 200px;
      height: 150px;
      background-color: pink;
      overflow: auto;
    }
    .news {
      height: 30px;
    }
  </style>
</head>
<body>
  <div id='test'></div>
  <script src='../js/react.development.js'></script>
  <script src='../js/react-dom.development.js'></script>
  <script src='../js/babel.min.js'></script>
  <script type='text/babel'>
    class NewsList extends React.Component {
      state = {
        newsArr: []
      }
      componentDidMount() {
        setInterval(() => {
          const {newsArr} = this.state
          const news = '新闻' + (newsArr.length+1)
          this.setState({newsArr: [news, ...newsArr]})
        }, 1000)
      }
      getSnapshotBeforeUpdate() {
        return this.refs.list.scrollHeight
      }
      componentDidUpdate(preprops, prestate, height) {
        this.refs.list.scrollTop += this.refs.list.scrollHeight - height
      }
      render() {
        return (
          <div className="list" ref="list">
            {
              this.state.newsArr.map((item, index) => {
                return <div key={index}>{item}</div>
              })
            }
          </div>
        )
      }
    }
    ReactDOM.render(<NewsList/>, document.getElementById('test'))
  </script>
</body>
</html>